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Apache XML Security for Java supports XML-Signature Syntax and Processing, W3C Recommendation 12 February 2002, and XML Encryption Syntax and Processing, W3C Recommendation 10 December 2002. As of version 1.4, the library supports the standard Java API JSR-105: XML Digital Signature APIs.
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/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.xml.security.c14n.implementations;

import java.lang.System.Logger;
import java.lang.System.Logger.Level;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

import org.w3c.dom.Attr;
import org.w3c.dom.Node;

/**
 * A stack based Symbol Table.
 *
For speed reasons all the symbols are introduced in the same map,
 * and at the same time in a list so it can be removed when the frame is pop back.
 */
public class NameSpaceSymbTable {

    private static final Logger LOG = System.getLogger(NameSpaceSymbTable.class.getName());

    private static final String XMLNS = "xmlns";
    private static final SymbMap initialMap = new SymbMap();

    static {
        NameSpaceSymbEntry ne = new NameSpaceSymbEntry("", null, true, XMLNS);
        ne.lastrendered = "";
        initialMap.put(XMLNS, ne);
    }

    /**The map between prefix-> entry table. */
    private SymbMap symb;

    /**The stacks for removing the definitions when doing pop.*/
    private final List level = new ArrayList<>();
    private boolean cloned = true;

    /**
     * Default constructor
     **/
    public NameSpaceSymbTable() {
        //Insert the default binding for xmlns.
        try {
            symb = initialMap.clone();
        } catch (CloneNotSupportedException e) {
            LOG.log(Level.ERROR, "Error cloning the initial map");
        }
    }

    /**
     * Get all the unrendered nodes in the name space.
     * For Inclusive rendering
     * @param result the list where to fill the unrendered xmlns definitions.
     **/
    public void getUnrenderedNodes(Collection result) {
        for (NameSpaceSymbEntry nsEntry : symb.entrySet()) {
            //put them rendered?
            if (!nsEntry.rendered && nsEntry.n != null) {
                nsEntry = nsEntry.clone();
                needsClone();
                symb.put(nsEntry.prefix, nsEntry);
                nsEntry.lastrendered = nsEntry.uri;
                nsEntry.rendered = true;

                result.add(nsEntry.n);
            }
        }
    }

    /**
     * Push a frame for visible namespace.
     * For Inclusive rendering.
     **/
    public void outputNodePush() {
        push();
    }

    /**
     * Pop a frame for visible namespace.
     **/
    public void outputNodePop() {
        pop();
    }

    /**
     * Push a frame for a node.
     * Inclusive or Exclusive.
     **/
    public void push() {
        //Put the number of namespace definitions in the stack.
        level.add(null);
        cloned = false;
    }

    /**
     * Pop a frame.
     * Inclusive or Exclusive.
     **/
    public void pop() {
        int size = level.size() - 1;
        Object ob = level.remove(size);
        if (ob != null) {
            symb = (SymbMap)ob;
            if (size == 0) {
                cloned = false;
            } else {
                cloned = level.get(size - 1) != symb;
            }
        } else {
            cloned = false;
        }
    }

    final void needsClone() {
        if (!cloned) {
            level.set(level.size() - 1, symb);
            try {
                symb = symb.clone();
            } catch (CloneNotSupportedException e) {
                LOG.log(Level.ERROR, "Error cloning the symbol map");
            }
            cloned = true;
        }
    }


    /**
     * Gets the attribute node that defines the binding for the prefix.
     * @param prefix the prefix to obtain the attribute.
     * @return null if there is no need to render the prefix. Otherwise the node of
     * definition.
     **/
    public Attr getMapping(String prefix) {
        NameSpaceSymbEntry entry = symb.get(prefix);
        if (entry == null) {
            //There is no definition for the prefix(a bug?).
            return null;
        }
        if (entry.rendered) {
            //No need to render an entry already rendered.
            return null;
        }
        // Mark this entry as render.
        entry = entry.clone();
        needsClone();
        symb.put(prefix, entry);
        entry.rendered = true;
        entry.lastrendered = entry.uri;
        // Return the node for outputting.
        return entry.n;
    }

    /**
     * Gets a definition without mark it as render.
     * For render in exclusive c14n the namespaces in the include prefixes.
     * @param prefix The prefix whose definition is needed.
     * @return the attr to render, null if there is no need to render
     **/
    public Attr getMappingWithoutRendered(String prefix) {
        NameSpaceSymbEntry entry = symb.get(prefix);
        if (entry == null) {
            return null;
        }
        if (entry.rendered) {
            return null;
        }
        return entry.n;
    }

    /**
     * Adds the mapping for a prefix.
     * @param prefix the prefix of definition
     * @param uri the Uri of the definition
     * @param n the attribute that have the definition
     * @return true if there is already defined.
     **/
    public boolean addMapping(String prefix, String uri, Attr n) {
        NameSpaceSymbEntry ob = symb.get(prefix);
        if (ob != null && uri.equals(ob.uri)) {
            //If we have it previously defined. Don't keep working.
            return false;
        }
        //Creates and entry in the table for this new definition.
        NameSpaceSymbEntry ne = new NameSpaceSymbEntry(uri, n, false, prefix);
        needsClone();
        symb.put(prefix, ne);
        if (ob != null) {
            //We have a previous definition store it for the pop.
            //Check if a previous definition(not the inmidiatly one) has been rendered.
            ne.lastrendered = ob.lastrendered;
            if (ob.lastrendered != null && ob.lastrendered.equals(uri)) {
                //Yes it is. Mark as rendered.
                ne.rendered = true;
            }
        }
        return true;
    }

    /**
     * Adds a definition and mark it as render.
     * For inclusive c14n.
     * @param prefix the prefix of definition
     * @param uri the Uri of the definition
     * @param n the attribute that have the definition
     * @return the attr to render, null if there is no need to render
     **/
    public Node addMappingAndRender(String prefix, String uri, Attr n) {
        NameSpaceSymbEntry ob = symb.get(prefix);

        if (ob != null && uri.equals(ob.uri)) {
            if (!ob.rendered) {
                ob = ob.clone();
                needsClone();
                symb.put(prefix, ob);
                ob.lastrendered = uri;
                ob.rendered = true;
                return ob.n;
            }
            return null;
        }

        NameSpaceSymbEntry ne = new NameSpaceSymbEntry(uri, n, true, prefix);
        ne.lastrendered = uri;
        needsClone();
        symb.put(prefix, ne);
        if (ob != null && ob.lastrendered != null && ob.lastrendered.equals(uri)) {
            ne.rendered = true;
            return null;
        }
        return ne.n;
    }

    public int getLevel() {
        return level.size();
    }

    public void removeMapping(String prefix) {
        NameSpaceSymbEntry ob = symb.get(prefix);

        if (ob != null) {
            needsClone();
            symb.put(prefix, null);
        }
    }

    public void removeMappingIfNotRender(String prefix) {
        NameSpaceSymbEntry ob = symb.get(prefix);

        if (ob != null && !ob.rendered) {
            needsClone();
            symb.put(prefix, null);
        }
    }

    public boolean removeMappingIfRender(String prefix) {
        NameSpaceSymbEntry ob = symb.get(prefix);

        if (ob != null && ob.rendered) {
            needsClone();
            symb.put(prefix, null);
        }
        return false;
    }
}

/**
 * The internal structure of NameSpaceSymbTable.
 **/
class NameSpaceSymbEntry implements Cloneable {

    final String prefix;

    /**The URI that the prefix defines */
    final String uri;

    /**The attribute to include.*/
    final Attr n;

    /**The last output in the URI for this prefix (This for speed reason).*/
    String lastrendered = null;

    /**This prefix-URI has been already render or not.*/
    boolean rendered = false;

    NameSpaceSymbEntry(String name, Attr n, boolean rendered, String prefix) {
        this.uri = name;
        this.rendered = rendered;
        this.n = n;
        this.prefix = prefix;
    }

    /** {@inheritDoc} */
    @Override
    public NameSpaceSymbEntry clone() { //NOPMD
        try {
            return (NameSpaceSymbEntry)super.clone();
        } catch (CloneNotSupportedException e) {
            return null;
        }
    }
}

class SymbMap implements Cloneable {
    int free = 23;
    NameSpaceSymbEntry[] entries;
    String[] keys;

    SymbMap() {
        entries = new NameSpaceSymbEntry[free];
        keys = new String[free];
    }

    void put(String key, NameSpaceSymbEntry value) {
        int index = index(key);
        Object oldKey = keys[index];
        keys[index] = key;
        entries[index] = value;
        if ((oldKey == null || !oldKey.equals(key)) && --free == 0) {
            free = entries.length;
            int newCapacity = free << 2;
            rehash(newCapacity);
        }
    }

    List entrySet() {
        List a = new ArrayList<>();
        for (NameSpaceSymbEntry nsEntry : entries) {
            if (nsEntry != null && !nsEntry.uri.isEmpty()) {
                a.add(nsEntry);
            }
        }
        return a;
    }

    protected int index(Object obj) {
        Object[] set = keys;
        int length = set.length;
        //abs of index
        int index = (obj.hashCode() & 0x7fffffff) % length;
        Object cur = set[index];

        if (cur == null || cur.equals(obj)) {
            return index;
        }
        length--;
        do {
            index = index == length ? 0 : ++index;
            cur = set[index];
        } while (cur != null && !cur.equals(obj));
        return index;
    }

    /**
     * rehashes the map to the new capacity.
     *
     * @param newCapacity an int value
     */
    protected void rehash(int newCapacity) {
        int oldCapacity = keys.length;
        String[] oldKeys = keys;
        NameSpaceSymbEntry oldVals[] = entries;

        keys = new String[newCapacity];
        entries = new NameSpaceSymbEntry[newCapacity];

        for (int i = oldCapacity; i-- > 0;) {
            if (oldKeys[i] != null) {
                String o = oldKeys[i];
                int index = index(o);
                keys[index] = o;
                entries[index] = oldVals[i];
            }
        }
    }

    NameSpaceSymbEntry get(String key) {
        return entries[index(key)];
    }

    @Override
    public SymbMap clone() throws CloneNotSupportedException  {
        SymbMap copy = (SymbMap) super.clone();
        copy.entries = new NameSpaceSymbEntry[entries.length];
        System.arraycopy(entries, 0, copy.entries, 0, entries.length);
        copy.keys = new String[keys.length];
        System.arraycopy(keys, 0, copy.keys, 0, keys.length);

        return copy;
    }
}